Drill bit having rotating stand-off elements



United States Patent 72] lnventor Horst 11. Hasiba Pittsburgh, Pa. [21] Appl. No. 840,703 [22] Filed July 10, 1969 [45] Patented Dec. 22, 1970 73] Assignee Gull Research & Development Company Pittsburgh, Pa. a corporation of Delaware [54] DRILL BIT HAVING ROTATING STAND-OFF ELEMENTS 8 Claims, 6 Drawing Figs. [52] US. (I 175/393, 175/422 [51] Int. Cl. ..E2lc 15/00, E21c 13/01; E2lb7/18 [50] Field of Search 175/418, 417, 409--411, 380, 422, 393

[56] References Cited UNITED STATES PATENTS 3,140,748 7/1964 Engle et a1. 175/410 3,269,470 8/1966 Kelly 175/410 3,393,756 7/1968 Mori l75/422X 3,414,070 12/1968 Pekarek 175/393 3,469,642 9/1969 Goodwin et al l75/422X Primary Examiner-David H. Brown Attorneys-Meyer Neishloss, Deane E. Keith and Paul L.

Tiilson ABSTRACT: A drill bit for hydraulic jet-drilling having a hollow body open at one end to receive an abrasive-laden drilling liquid and closed at the other end. Nozzles extend through the closed end to discharge high-velocity streams of the drilling liquid from the drill bit against the material to be drilled. Standoff elements rotatably mounted in the lower end of the drill bit extend downwardly from the lower end of the drill bit to position the nozzle outlets at the desired distance from the material to be drilled. Preferred standoff elements are shaped and positioned to extend part of the way into grooves cut by the high-velocity streams and eccentrically load ridges between the grooves.

Q PATENTEnuiczzim 3548-860 SHEEIZDFZ' 4 54 INVENTOR.

2 HORST HAS/BA DRILL BIT HAVING ROTATING STAND-OFF ELEMENTS This invention relates to drilling and more particularly to a drill bit for hydraulic jet-drilling in which penetration of the material drilled is by means of high-velocity streams of abra sive-laden liquid.

In the conventional rotary drilling process for drilling wells, a drill bit mounted on the lower end of a drill stem is rotated against the bottom of the borehole while a-fluid, usually a drilling mud, is circulated down the hole on one side of the drill stem and up. the hole on the other side to remove cuttings from the hole. Ordinarily the drilling mud is circulated down through the drill stem, out through nozzlesin the drill bit, and up through the annulus between the drill stem and the borehole wall. The drill bit mechanically breaks particles of rock from the bottom of the hole.

The rotary drilling process has been highly successful in drilling soft formations and formations of medium hardness, but has not been as, successful in drilling hard formations. In addition to causing a lower rate of penetration, hard formations cause rapid wear of the drill bits and make necessary frequent round trips to replace the bit. The lost drilling time during the round trips increases the time a drilling rig must stay at the well site and thereby increases the cost of drilling.

One method that has been developed recently for the drilling of hard formations is the hydraulic jetdrilling process. In that process the bottom of the borehole is eroded by a plurality of streams of an abrasive-laden liquid discharged at extremely high velocity from nozzles in adrill bit connected to the bottom of a rotating drill stern. In a preferred hydraulic jetdrilling method, the streams of abrasive-laden liquids cut a central hole and plurality of concentric grooves in the bottom of the borehole and the drill bit engages the ridges separating the grooves to break large particles of rock from the ridges and thereby increase the drilling rate. Although the hydraulic jet-drilling method has shown advantages over conventional rotary drilling resulting from increases in rate of penetration and reduction in wear of the drill bit, further increases in the drilling rate are desirable to reduce the cost of drilling.

One problem encountered in hydraulic jet drilling is erosion of the drill bit by abrasive particles rebounding from the bottom of the borehole and striking the bottom of the bit. Erosion of the bottom of the bit is reduced by covering those portions of the bottom of the bit exposed to rebounding abrasive particles with a hard, abrasion-resistant material such as a tungsten carbide alloy. Erosion of the bottom of the drill bit is further reduced by maintaining a minimum stand-off distance between the bottom of the borehole and the outlets of the nozzles through which the drilling liquid is discharged. Standoff elements extending downwardly from the bottom of the drill bit engage the bottom of the borehole and support the bit at the desired distance above the bottom of the borehole.

This invention resides in a bit for hydraulic jet drilling of boreholes through hard subsurface formations in which the standoff elements extending downwardly from the lower surface of the drill bit to maintain the distance from the bottom of the borehole to the nozzle outlets are rotatably mounted in the bit. The rotatably mounted standoff elements have a smooth surface that rolls along the upper surface'of the ridges to apply a load to the ridges without cutting into the ridges. In the preferred form of this invention, the standoff elements are positioned and shaped to extend into grooves cut in the bottom of the borehole by high-velocity streams of drilling liquid discharged through the nozzles in the drill bit and ride on the ridges separating the grooves whereby the standoff elements exert a lateral force on the ridges.

In the drawings:

FIG. 1 is a bottom plan view of a drill bit constructed in accordance with this invention.

FIG. 2 is a longitudinal sectional view taken along section line II-II in FIG. 1.

FIG. 3 is a vertical sectional view of one embodiment of a tapered, rotatably mounted standoff element.

FIG. 4 is a view partially in vertical section along section line IV-IV in FIG. 3 of the embodiment of the standoff element illustrated in FIG. 3.

FIG. 5 is a bottom view of a drill bit having relief passages in its lower surface and provided with rotatably mounted standoff elements.

FIG. 6 is a partial vertical sectional view taken along section line VI-VI in FIG. 5 with the drill bit in an inverted position.

Referring to FIG. 2 of the drawings, a drill bit indicated generally by reference numeral 10 is illustrated having a body 12 from which a threaded shank 14 extends upwardly for connection to the lower end 16 of a drill stem. A central passage 18 extends longitudinally through the shank l4 and communicates with a throat 20 in the drill bit body 12. Throat 20 opens into an enlarged central opening 22 in the drill bit body. As shown in FIG. 1, the drill bit body is of generally equilateral triangular horizontal cross section formed by three flat faces 24 joining curved portions 26 on the periphery of the drill bit. This invention is not limited to any particular horizontal cross section shape, but it has been found that drill bits utilizing this invention will operate more smoothly if of generally symmetrical cross section. The flat surfaces result in a nonround shape that provides space between the bit and the borehole wall for the removal of cuttings from the borehole.

Referring to FIG. 2 of the drawings, the lower end of central opening 22 is closed by the bottom of the drill bit body 12. To reduce erosion of the drill bit body during the drilling operation the bottom surface 28 of body 12 is covered by a backsplash plate 30 of an abrasion-resistant material such as tungsten carbide secured in place by brazing or silver soldering. A plurality of nozzles 32, specifically identified in the drawings by the reference numeral 32 and a letter which depends on the location of the nozzle, extends through the bot tom of the drill bit body 12 and the backsplash plate 30 for discharge of abrasive-laden drilling liquid in the manner hereinafter described. The outlets of the nozzle 32 are in the plane of the lower surface of backsplash plate 30. Nozzles 32 are preferably constructed of an abrasion-resistant material such as a tungsten carbide alloy and have an outlet 3/ 16 inch to 3/32 inch in diameter.

It is desirable that the nozzles 32 be positioned and oriented to cut a central hole and a plurality of concentric grooves in the bottom of the borehole. The outermost groove has an outer diameter larger than the diameter of the drill bit body 12 to permit descent of the drill bit as drilling progresses. The ridges in the bottom of the boreholeseparating the grooves should be relatively narrow, having a width less than about a inch, to allow them to be broken by a light load placed on the drill bit. In the drill bit illustrated in FIG. 1, innermost nozzles 32a slope rather sharply inward to discharge a high-velocity jet stream that will cut a central hole extending below the center of the drill bit. The next series of nozzles 32b located farther than nozzles 32a from the center of the drill bit slopes inwardly less sharply than nozzles 32a and cuts a groove separated from the central hole by an intervening ridge of the material being drilled. A third series of inwardly sloping nozzles 32c is spaced at a larger distance from the center of rotation of the drill bit than nozzles 32b and cuts a groove separate from the groove cut by the drilling liquid discharged from nozzles 32b. The next two series of nozzles 32d and 32e slope outwardly and cut separate grooves. A final series of nozzles 32f slopes sharply outwardly to discharge a high-velocity stream of jet drilling liquid that strikes the bottom of the borehole outwardly beyond the periphery of the drill bit body to form a borehole of a gauge larger than the diameter of the drill bit.

Rotatably mounted in the bottom of the drill bit are spherical standoff elements identified generally by the reference numeral 34. Standoff element 34a is positioned slightly closer to the center of the drill bit than the outlet of inwardly sloping nozzles 32b to ride on the ridges bounding the groove cut by the drilling liquid discharged from those nozzles. Similarty. standoff element 34b is positioned directly above the groove cut by the drilling liquid discharged from nozzles 32c, standoff element 34c directly above the groove cut by the drilling liquid discharged from nozzles 32d and standoff element 34d directly above the groove cut by the drilling liquid discharged from nozzles 32c. Standoff elements 34 are constructed of an abrasive-resistant material, such as a tungsten carbide alloy, and have a diameter such that they will extend 5 4 inch to 1% inches below the lower surface of backsplash plate 30.

Referring to FIG. 2 in which standoff element 34c is illustrated in vertical section, a socket 36 drilled in the lower end of the drill bit body 12 receives an insert 38. A plate 39 in the upper end of the socket is separated from a tungsten carbide standoff element seat 42 by a compressible ring 40. Standoff element seat 42 is lapped with a ball having the same nominal size as the spherical loading element to produce a surface that will support the loading element in a manner permitting it to rotate freely. The spherical-loading element is held in place by a retaining ring 44 covered by a tungsten carbide face plate 46. The entire assembly shown in FIG. 2 is held in place in the drill bit body 12 by a pin 50 extending through the side of the drill bit body and the insert 38 into the seat 42. The face plate 46 and retaining ring 44 can be held in place by any suitable means such as screws, as illustrated in FIG. 1 for some of the standoff elements, or a suitable cement such as an epoxy cement.

In the operation of the drill bit of this invention, the drill stem and drill bit are rotated and a drilling liquid, for example, an aqueous liquid-containing paper fibers and clay to aid in suspending abrasive particles is pumped down the drill stem 16 into the passage 18 in the shank 14 of the drill bit. Preferred abrasive particles are particles of cast iron or steel shot or grit having a size in the range of about to 80 mesh. The drilling liquid is at a high pressure exceeding about 4,000 p.s.i. in the central opening 22 so that the drilling liquid will be discharged from the nozzles at a velocity exceeding about 650 feet per second. Particles eroded from the bottom by the highvelocity streams of drilling liquid discharged from nozzles 32 and larger cuttings broken from the ridges by the standoff elements are carried by the liquid discharged through the nozzles up through the annulus between the borehole wall and the drill stem to the top of the hole. Flat surfaces 24 result in large openings between the borehole wall and the drill bit through which the cuttings pass readily.

As indicated above, the high-velocity stream of drilling liquid cuts a central hole surrounded by concentric grooves in the bottom of the borehole. The standoff elements roll on the ridges separating the grooves and apply a compressive load that breaks the ridges. Because of the spherical shape of the preferred standoff elements, the force they apply to the ridges as a result of weight on the bit has a lateral component which places a portion of the rock in the ridges under tension and thereby facilitates breaking of the ridges. Anrimportant advantage of the rotating standoff elements is reduction of the alternate cooling and heating that occurs in stationary standoff elements because of the periodic variations in friction between such standoff elements and the rock. The drill bit of this invention has been found to reduce the torque required to rotate the drill stem and the drill bit when weight is applied to the drill bit. The rotating standoff elements also cause smoother operation of the drill bit with a consequent reduction of stresses applied to the drill bit and the drill string.

The rotating standoff elements illustrated in FIGS. 3 and 4 have tapered surfaces which permit the standoff element to enter farther into the grooves cut by the drilling liquid discharged from the nozzles and apply a larger lateral force to the ridges separating the grooves. Referring to FIG. 3, a socket 60 is drilled into the lower end of drill bit body 12 to receive an insert 62 adapted to receive the tapered rotating element 64, a seat 66 and a resilient ring 68 compressed between the seat 66 and a base plate 70. The lower end of the insert 62 is secured to a retaining ring 72 through which the rotating loading element 64 extends. The assembly illustrated in FIGS. 3 and 4 can be held in place in the socket 62 by any suitable means such as the pin illustrated in FIG. 2 or an epoxy cement. The operation of the loading element illustrated in FIGS. 3 and 4 is identical to that illustrated in FIG. 2.

The rotating loading elements of this invention can be used advantageously in hydraulic jet-drilling bits having relief channels through which cuttings from the bottom of the borehole can readily pass for circulation up the borehole with a minimum of regrinding. Referring to FIG. 5 of the drawings, the bottom of a drill bit body is illustrated with recessed channels between plateaus 82. Plateaus 82 are preferably constructed with an abrasion-resistant face plate 84 secured to projections 86 extending from the bottom of the drill bit body. The outlets of nozzles 88 are in the plane of the lower surface 90 of the face plate 84. The rotating loading elements 92 are held in placeon seats 94 by retaining rings 96. Seats 94 and retaining rings 96 fit in inserts 98 which in turn fit within a socket 100 in the lower end of the drill bit body. As in the embodiment of the invention illustrated in FIGS. 1 and 2, the loading elements 92 are located to be directly above grooves cut in the bottom of the borehole by high-velocity streams of drilling liquid discharged through nozzles 88. In the embodiment of the invention illustrated in FIGS. 5 and 6, retaining rings 96 and inserts 98 are secured in sockets 100 by a suitable cement such as epoxy cement.

Iclaim:

1. In a drill bit for hydraulic jet-drilling of boreholes, said drill bit having a hollow body closed at its lower end by a bottom member, and nozzles extending through the bottom member and terminating in the lower surface thereof, the improvement comprising standoff elements rotatably mounted in the bottom member of the bit and extending a distance of V4 inch to 1% inches below said bottom surface.

2. A drill bit as set forth in claim 1 characterized by the standoff elements being spherical and partially recessed in the bottom member of the drill bit.

3. A drill bit as set forth in claim 1 in which the standoff elements are substantially diamond-shaped in section along a plane including the axis of rotation and circular in section perpendicular to the axis of rotation.

4. A drill bit for the hydraulic jet drilling of hard formations by high-velocity streams of abrasive-laden drilling liquid comprising a hollow drill bit body closed at its lower end, nozzles extending through the lower end of the drill bit body positioned such that high-velocity jet streams discharged through the noules cut a central hole and a plurality of concentric grooves in the bottom of the borehole separated by ridges, and standoff elements rotatably mounted in the lower end of the drill bit positioned to extend into grooves cut in the bottom of the borehole and ride on ridges in the bottom of the borehole between such grooves, said standoff elements being recessed in the lower end of the drill bit and extending below the lower surface thereof a distance of 54 inch to l% inches, said nozzles having their outlets in the plane of the lower surface of the lower end of the drill bit.

5. A drill bit as set forth in claim 4 in which the standoff elements are spherical.

6. A drill bit as set forth in claim 4 in which the standoff elements are substantially diamond-shaped in section along a plane including the axis of rotation and circular in section perpendicular to the axis of rotation, and the axis of rotation is horizontal and is along the short axis of the diamond-shaped standoff element.

7. A drill bit for the hydraulic jet drilling of hard formations by high-velocity streams of abrasive-laden drilling liquid comprising a hollow drill bit body closed at its lower end, nozzles extending through the drill bit body and terminating in the plane of the lower surface of the lower end thereof to discharge high-velocity streams at intervals over the bottom of the borehole to cut grooves therein, sockets in the lower end of the body, standoff element seats positioned in the sockets, standoff elements partially within the sockets and engaging the standoff element seats, said seats being lapped to fit the standoff elements, a retainer in the lower end of the socket engaging the standoff element and holding it in place on the seat, means to secure the retainers to the bottom member of the drill bit, said standofi' elements being free to rotate on the seats and extending a distance of A inch to 1% inches below the lower surface of the lower end of the drill bit.

8. A drill bit for hydraulic jet drilling of hard formations by discharging highnvelocity streams of an abrasive-laden drilling liquid against the formation comprising a hollow drill bit body closed at its lower end, three substantially sectorially shaped plateaus extending downwardly from the lower end of the drill bit, recessed relief channels interconnecting near the center of the lower end of the drill bit and extending substantially radially toward the perimeter thereof to separate the plateaus, a backsplash plate of abrasion-resistant material secured to the lower end of each of the plateaus, nozzles extending downwardly through the lower end of the drill bit, the plateaus, and the backsplash plates and terminating in the plane of the lower surface of the backsplash plates, sockets extending through each of the backsplash plates and into each plateau to receive standoff elements rotatably mounted within each socket and positioned to place one standoff element at a small distance from the center of rotation of the drill bit, two standofi elements at a second and larger'radial distance from the center of rotation of the drill bit, and three standoff elements at a third and larger radial distance from the center of rotation of the drill bit, a retainer in each of the sockets slidably engaging the standoff elements below the center of rotation to hold the standoff elements in a recessed position in the sockets at which the standoff elements extend a distance of A inch to 1% inches below the lower surface of the backsplash plate, and means for holding the retainers in place in the sockets. 

